As the recording density of a magnetic recording device, as represented by a disk drive unit, becomes higher, further improvement has been required in the performance of a magnetic head and a magnetic recording medium, especially, in the magnetic recording medium. To increase the recording density of a magnetic recording device, it is necessary to decrease the size of the magnetic fine particles that constitute the magnetic recording medium. Making the magnetic fine particles smaller, however, causes the problem that the magnetic fine particles drop in the thermal stability of magnetization.
To solve this problem, it is effective to increase the anisotropic energy of the magnetic fine particles. However, increasing the anisotropic energy of the magnetic fine particles leads to an increase in anisotropic magnetic field (high coercivity) of the magnetic recording medium. As a result, the magnetic head cannot write data to the magnetic recording medium when the anisotropic magnetic field of the medium exceeds the write field limit.
Recently, as a method for solving the problem of thermal stability, so-called a thermally-assisted magnetic recording (TAMR) technique is proposed. In the technique, a magnetic recording medium formed of a magnetic material with a high coercivity is used so as to stabilize the magnetization, then anisotropic magnetic field of a portion of the medium, where data is to be written, is reduced by heating the portion; just after that, writing is performed by applying write field to the heated portion. The area where data is written subsequently falls in temperature and rises in anisotropic magnetic field to increase the thermal stability of magnetization. Hereinafter, a magnetic head for use in TAMR will be referred to as a thermally-assisted magnetic head (TAMH).
In this TAMR technique, there has been generally used a method in which a magnetic recording medium is irradiated and thus heated with a light such as near-field light. A known method for generating near-field light is to use a plasmon generator, which is a piece of metal that generates near-field light from plasmons excited by irradiation with light. The light for use to generate near-field light is typically guided through a waveguide, which is provided in the slider, to the plasmon generator disposed near the medium facing surface, that is, a surface of the slider that faces the magnetic recording medium.
To supply the light for use to generate near-field light to the waveguide, a laser diode may be secured to the slider to allow laser light emitted from the laser diode to be incident on the incidence end of the waveguide provided in the slider, as disclosed in U.S. Patent Application Publication No. 2011/0228650 A1, for example.
U.S. Patent Application Publication No. 2011/0228650 A1 discloses a thermally-assisted magnetic recording head including a slider having a waveguide, and a light source unit. The light source unit includes a laser diode and a unit substrate for supporting the laser diode. The unit substrate is bonded to the slider, being positioned so that emitted light from the laser diode will be incident on the incidence end of the waveguide. Solder, for example, is used to bond the unit substrate to the slider.
In the process of manufacturing the thermally-assisted magnetic recording head including the laser diode, the unit substrate and the slider as described above, it is important that the unit substrate be accurately positioned with respect to the slider so that emitted light from the laser diode will be accurately incident on the incidence end of the waveguide.
U.S. Patent Application Publication No. 2011/0228650 A1 discloses a positioning method that allows the unit substrate to be positioned with respect to the slider in the following manner. In the positioning method, emitted light from the laser diode is allowed to be incident on the incidence end of the waveguide, the intensity of light emitted from the emitting end of the waveguide is detected, and the unit substrate is positioned with respect to the slider so that the aforementioned intensity becomes the maximum.
While, the method of positioning the unit substrate with respect to the slider by the light intensity just search a light intensity peak position, but can not provide us the actual alignment position information, that is, the actual alignment position can not be evaluated.
Therefore, a cross section surface observation method is provided to evaluate alignment position of the bonded sample of a slider 22′ and a light source unit 24′, referring to FIGS. 1 to 4. Concretely, FIG. 1 and FIG. 2 show a horizontal direction cross section view of the slider 22′ and the light source unit 24′, an position offset X1′ can be evaluated according to the positions of the centerline L1′ of a laser diode stripe 2422′ of a light source 242′ and the centerline L2′ of the waveguide 222′ embedded in the slider 22′ at a horizontal direction, that is, this method just can evaluate the actual alignment position thereof in the horizontal direction, but can not provide us the actual alignment position in a perpendicular direction at the same time. To the contrary, FIG. 3 and FIG. 4 show a perpendicular direction cross section view of the slider 22′ and the light source unit 24′, which just can evaluate the actual alignment position thereof in the perpendicular direction, but can not provide us the actual alignment position thereof in the horizontal direction at the same time. Namely, cross section surface observation method just can evaluate alignment accuracy in one dimensional direction, but not in two dimensional directions. In addition, the cross section surface observation method was the only way to evaluate the accuracy of the alignment position so far. But it takes long time to prepare the samples and machine. Therefore, we could not evaluate lots of samples' alignment accuracy at the same time.
In the method of performing thermally-assisted magnetic recording, it is important to stably supply light with sufficient intensity to a desired position on the magnetic recording medium. Therefore, it is necessary to secure high alignment accuracy for fixing a light source unit to a slider. Reduction in alignment accuracy causes reduction in heating efficiency with respect to a magnetic recording medium, and it is serious issue in thermally-assisted magnetic recording. From the reason, it is desirable to provide a method capable of easily and accurately testing and manufacturing a thermally-assisted magnetic recording head excellent in write efficiency. Hence, it is desired to provide a method of testing a TAMH to overcome the above-mentioned drawbacks.